Regio- and enantioselective allylic amination of achiral allylic esters catalyzed by an iridium-phosphoramidite complex
A new catalytic asymmetric process, the iridium-catalyzed enantioselective allylic amination of (E)-cinnamyl and terminal aliphatic allylic carbonates, was developed by exploring complexes of chiral phosphoramidites. The reaction provided branched secondary and tertiary allylic amines in high yields with excellent regio- and enantioselectivity (13 examples over 94% ee). Although the reactions in polar solvent such as DMF, EtOH, and MeOH were fast, they gave low enantiomeric excesses. In contrast, reactions in THF displayed the most suitable balance of rate and enantioselectivity. Both the binaphthol unit and the disubstituted amine in the phosphoramidite affected reactivity and selectivity, and complexes of O,O‘-(R)-(1,1‘-dinaphthyl-2,2‘-diyl)-N,N‘-di-(R,R)-1-phenylethylphosphoramidite provided the highest reactivity and selectivity. Primary and cyclic secondary amines reacted at room temperature, and acyclic diethylamine reacted at 50 °C. p-Methoxy-substituted cinnamyl carbonate reacted similarly to the unsubstituted cinnamyl carbonate, but the o-methoxy-substituted substrate gave lower enantiomeric excess. High ee's were also observed for the products from the reaction of furanyl- and alkyl-substituted (E)-allylic carbonates.
Read more on publisher's site.